TEMPORAL DYNAMICS, ANTIMICROBIAL RESISTANCE AND PHYLOGENETIC RELATIONSHIPS OF BACTERIAL TAXA IN IRRIGATION WATER SOURCES AND RELEVANCE TO FOOD SAFETY
Micallef, Shirley SAM
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As climate change continues to stress freshwater resources, we have a pressing need to identify alternative (nontraditional) sources of microbially safe water for irrigation of fresh produce. Unfortunately, open water sources are often contaminated with many known human pathogens such as E. coli, Salmonella and Listeria and unknown/understudied pathogens such as Aeromonas that are associated with foodborne outbreaks. To facilitate the adoption of microbiologically safe irrigation water sources, a comprehensive study on the prevalence and virulence potential of human pathogens and their transferability to fruit and fresh produce vegetables was conducted. The effect of irrigation water types on crop surface microbial community structure, presence of virulence factors and antimicrobial resistance were investigated to evaluate the potential of transfer of pathogenic and antimicrobial resistant bacteria in humans. Initially, the prevalence of indicator bacteria was determined using culture methods and then microbiological water quality profiles (MWQP) was created to identify water sources that complied with the U.S Food Safety Modernization Act water standards. Next, using culture and molecular methods, investigation of the antimicrobial resistance profile of one known foodborne pathogen Escherichia coli retrieved over a two-year period was done. E. coli resistance against widely prescribed antibiotics, extended spectrum β-lactams, was determined phenotypically and genetically. The diversity, distribution and potential for pathogenesis of one understudied pathogen, Aeromonas, prevalent in a variety of typical or potential irrigation water sources and collected over a one-year period was investigated. The study revealed spatial and temporal patterns in species richness, evenness, virulence gene carriage and attachment behaviors on both biotic and abiotic surfaces, of this bacterial taxon. Finally, the effect of using highly treated reclaimed water and pond water on lettuce surface microbiomes was investigated. The study provided an integrated assessment of the shifts in microbial community that result from using different irrigation water sources for irrigation of lettuce. Understanding the ecology of lettuce associated microbiota can be useful to infer risks of transfer and establishment potential of possible pathogenic strains from irrigation water sources to minimally processed raw consumed fresh produce crops.